Aspen Plus start

We click on Start and select Programs, Aspen Tech, Aspen Engineering Suite, Aspen Plus 2004, and Aspen Plus User Interface. The window shown in Figure 2.26 opens. A Blank Simulation is selected, and clicking OK opens a blank flowsheet shown in Figure 2.27. 

The simulation of the above separation scheme is performed with Aspen Plus software [23]. The starting mixture is the acrylonitrile stream given in the last... 

Start with an equimolar amount of ethylene and hydrogen chloride and determine the equilibrium composition at 350°F and 250 psig using Aspen Plus. 

Most processes involve a recycle stream. The reason is that all the reactants do not react, and businesses cannot afford to throw the rest away. Furthermore, any leftovers have to be disposed of in an environmentally friendly manner, which costs money. Thus, engineers take the unreacted reactants and put them back in the start of the process and try again. This makes the mass balances a little more complicated, and it leads to iterative methods of solution, which are described in this chapter. The hrst part of this chapter uses Excel to solve mass balances with recycle streams. Situations in which the energy balances affect the mass balance are treated in Chapters 6 and 7, because these are best done using a process simulator such as Aspen Plus . 

If you run the problem, make a change in a parameter, and run the problem again, Aspen Plus will use the first solution as the starting guess for the second problem. If you do not want this to happen, choose Run/Reinitialize or the reinitialize button mJ, and the starting values are put back to the default values (flow rates are usually zero). You can also do the iterative calculations one unit at a time by choosing the Run/Step menu or Ctrl + F5 or the open triangle. 

The call back queries used in these steps are not purely queries to source databases. For example, the needed simulation results of the reactor are results of an aggregation function. In this sense the results are the results of a (highly complex) query on the data warehouse store. As simulating is a time consuming and expensive task we also store the results in the data warehouse for reuse. To gain access to the units the DB trader contains meta information about the CAPE-OPEN components. As a result of the usage of the CAPE-OPEN compliant units we do not need to handle very different simulators such as Aspen Plus, Pro/II or gPROMS, but only have to create the CAPE-OPEN objects used by the units. This especially concerns the material object for each substance contained in the input ports of the unit. The process data warehouse produces these CORBA objects and is then able to start the simulation of the unit. 

CHEOPS obtains this setup file in XML format from ModKit-l-. Tool wrappers are started according to this XML file. The input files required for the modeling tools Aspen Plus and gPROMS are obtained from the model repository ROME. CHEOPS applies a sequential-modular simulation strategy implemented as a solver component because all tool wrappers are able to provide closed-form model representations. The iterative solution process invokes the model evaluation functionality of each model representation, which refers to the underljdng tool wrapper to invoke the native computation in the modeling tool the model originated from. Finally, the results of all stream variables are written to a Microsoft Excel table when the simulation has terminated. 

We start by examining the feasibility of alternative feeding policies by steady state simulation in Aspen Plus. Figure 13.12 depicts the flowsheet. The key units are the reactor and the distillation column. We chose a PFR model, with 100% per-pass conversion of A. The reactant B is converted exactly in the same proportion as the amount of fresh A, but the excess is recovered by distillation and recycled. Further, we consider a distillation column with 10 stages and feed in the middle. 

To reiterate what was said at the start of this section, certain thermodynamic models cannot be used when plotting outside the MET due to the presence of logarithms of composition which cannot be evaluated for negative values. However, we can still use these models to see if the same or similar behavior is experienced within the MET. As an example, coasider the RCM plot for the acetone/ethanol/methanol system operating at 10 atm as shown in Figure 2.20. This plot was generated in Aspen Plus using the UNIQUAC thermodynamic model. 

When using ASPEN PLUS, the details of the convergence forms and the CONVERGENCE paragraph generated can be found in Chapter 17, Volume 2, of the ASPEN PLUS User Guide. See also the modules in ASPEN — Principles of Flowsheet Simulation —> Recycle on the multimedia CD-ROM that accompanies this book. For HYSYS.Plant, the user can consult the modules under HYSYS Principles of Flowsheet Simulation —> Getting Started... 

The user can either select an existing project in which to start a new scenario, or enter a new Project Name. The Project Name RADFRAC-IPE is assigned automatically from the ASPEN PLUS file name, however punctuation marks are not allowed, so enter the Project Name DECS instead. Note that the underscore and space characters are permitted. After pressing the OK button, the first of four dialog boxes, not shown here, appear. The first is the Project Properties dialog box, in which a Project Description and further remarks may be entered. A units of measure set is also chosen, which for this example is the Inch-Pound (IP) units set. 

Multicomponent flash distillation is a good place to start learning how to use a process simulator. The problems can easily become so conplicated that you don t want to do them by hand, but are not so complicated that the working of the simulator is a mystery. In addition, the simulator is unlikely to have convergence problems. Although the directions in this appendix are specific to Aspen Plus, the procedures and problems are adaptable to any process simulator. The directions were written for Aspen Plus V 7.2, 2010 but will probably apply with little change to newer versions when they are released. Additional details on operation of process simulators are available in the book by Seider et al. (2009) and in the manual and help for your process simulator. 

To get started, do external mass balances and calculate accurate values for the two bottoms flow rates assuming that the water and MEK products are both pure. Specify the bottoms flow rate of column 1 = 60, but do NOT specify bottoms in column 2. In column 2 start with D = 20 and increase D in steps, 30, 40, 50, 60, 70, and so forth without reinitializing. If you don t step up. Aspen Plus will have errors. 

The resulting Makeup flow rate will be extremely small since losses of solvent are small (after all, no one wants to drink ethylene glycol with their alcohol or their water). If you immediately use this value of solvent makeup as a feed to the system. Aspen Plus will not converge. Start with the value you were using previously and rapidly decrease it (say by factors of roughly 5 or 10). Until the solvent makeup stream is at the desired value for the external mass balance, the extra ethylene glycol will exit with the distillate (water product) from column 2. This occurs because Bottoms flow rate in column 2 is specified and the only place for the extra ethylene glycol to go is with the distillate from column 2. 

Lab 10. Aspen Plus uses RADFRAC with the Tray Rating option to do detailed tray and downcomer design. Start by setting up the problem below with RADFRAC. 

Although the MDEA/piperazine process can be modelled in a very similar fashion to MDEA-only (Section 2.3) using the ElecNRTL physical property approach in Aspen Plus, the ions of piperazine and their electrolyte reactions in Eqs. (14)-(17) are not contained in the Aspen Properties database. Therefore, the electrolyte wizard cannot be used to add the equations and their components, and instead they must be added in manually. Once the components have been added, the electrolyte reactions can then be manually added in the Chemistry section (be sure to include it in the same chemistry specification which also includes the MDEA electrolyte reactions). Note that newer versions of Aspen Plus now include a simple example for using this setup in the Examples folder (select ElecNRTL Rate Based PZ+MDEA Model.bkp). It is usually easier to start with this file and modify it for your own purposes than it is to enter the data manually. 

Follow the steps given in Section 3.1 to start up Aspen Plus. Instead of building up a new flowsheet, we need to first add EMC into the simulation. From the dropdown menu in Data, select Setup from the list as shown in Figure 3.62. The Data Browser window opens (Fig. 3.63). Previously we selected Flowsheet as the run type (Fig. 3.8). Instead, now we select Property Estimation as the run type. The next step is to go to the left-hand side of the Data Browser window and click Specifications under the Components list... 

The Aspen Plus backup file in this example is called flash.bkp so the Aspen D3mamics file is called flash.dynf. Starting this .dynf file in Aspen Dynamics opens the screen shown in Figure 4.23. There are three windows Process Flowsheet Window, Exploring, and Simulation Messages. The flowsheet is shown with the vessel, valves, and pump. 

Start the Aspen program, select Aspen Plus User Interface, and when the Connect to Engine window appears, use the default Server Type Local PC. Select Pipe under the Pressure Changes tab from the Equipment Model Library and then click on the flow sheet window where you would like the piece of equipment to appear. In order to add material streams to the simulation, select the material stream from the Stream Library. When the material stream option is selected, a number of arrows will appear on each of the unit operations. Red arrows indicate a required stream and blue arrows indicate an optional stream. 

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